Amylase calcium

Sometimes sodium or potassium chloride (0.18-1.0%) is added to the desizing bath for pancreative enzymes to get its full activity. For malt a-amylase calcium ion is effective and sequestering agent must be avoided in the desize bath. These salts are particularly used for desize mixture by affording heat protection to enzyme, increased stability of the enzyme and efficiency. On the other hand, heavy metal ions such as copper, iron etc. may combine with enzyme and inhibit its activity [8]. Sometimes hydrocarbon solvents such as xylene (50 ml/1) along with suitable emulsifier (4 g/1) are also added to facilitate removal of waxy components of the size. 

Amylase Calcium sulfate dihydrate Carbon, activated Cesium carbonate Cesium chloride Cesium sulfate Simethicone Sulfurous acid brewing, beer Peracetic acid brewing, cask sterilization Sodium bisulfite brick, refractories Chromium oxide (ic)... 

Low Temperature Process. The low temperature process was developed when B. licheniformis and B. stearothermophilus a-amylases became commercially available in the 1970s. These enzymes ate more thermostable, more acidutic, and requite less calcium for stabiUty than the B. subtilis enzyme used in the EHE process. Consequendy, the high temperature EHE heat treatment step was no longer requited to attain efficient Hquefaction. 

ThermalLkjucfaction Process. In the thermal Hquefaction process (see Eig. 1), a starch slurry containing no enzyme or added calcium is heated for several minutes. The slurry is slightly acidic and sufficient acid Hquefaction is achieved to reduce viscosity. The hydrolyzate (at essentially zero DE) is flash-cooled to 95—100°C, a-amylase is added, and the pH is adjusted. The reaction then goes to completion. 

Sodium propionate is also often used as an antifungal agent. Calcium is often preferable to sodium, both to reduce sodium levels in the diet and because calcium ions are necessary for the enzyme a-amylase to act on the starches in bread, making them available for the yeast, and improving the texture of the bread. Stale bread is caused by the starch amylose recrystallizing. The enzyme a-amylase converts some of this starch to sugars, which helps prevent recrystallization. 

Calcium propionate is often preferred as an antifungal agent, to reduce sodium levels in the diet, but also because calcium ions are necessary for the enzyme a-amylase to act on the starches in bread,... 

As mentioned above, certain metal ions may be necessary for activity or stability. Thus calcium is needed for bacterial a-amylase. Magnesium or cobalt is needed with glucose isomerase. Calcium stabilises the starch-liquifying bacterial a-amylases but inactivates the glucose isomerase that may be used subsequently. Many enzymes contain an additional non-... 

Even after extensive purification, the amylase of Aspergillus oryzae is relatively stable in aqueous solutions held at ordinary room temperature. Its lability increases with increasing temperatures and becomes very rapid between 50° and 60°. This loss of activity may be retarded by the presence of substrate and by the presence of calcium ions.4070... 

Examination of the ratios of the dextrinogenic to the saccharogenic activities of malted barley extracts before and after treatment shows that the results of the Ohlsson procedures23 are not always predictable.8 The concentration of the amylases in the extracts, and the kinds and concentrations of substances which accompany them, influence the results. The presence or the absence of calcium ions is an important factor. Calcium ions increase the inactivation of beta amylase of malted barley and protect the alpha amylase from inactivation at unfavorable temperatures and also at unfavorable hydrogen ion activities.28 With purification, both amylases become increasingly thermolabile and increasingly sensitive to unfavorable hydrogen ion activities.78... 

The alpha amylase of malted barley, the amylase of Aspergillus oryeae and pancreatic amylase all are thermolabile proteins that rapidly lose their amylase activities upon exposure to unfavorable temperatures, to unfavorable hydrogen ion activities, or to other unfavorable chemical environments. The loss of amylase activity in aqueous solutions increases with increasing temperatures and is exceedingly rapid for each of these amylases at 50°. The inactivation of each of these amylases at unfavorable temperatures or at unfavorable hydrogen ion activities may be retarded by the presence of suitable concentrations of calcium ions. 

To understand the inhibition of a-amylase by peptide inhibitors it is crucial to first understand the native substrate-enzyme interaction. The active site and the reaction mechanism of a-amylases have been identified from several X-ray structures of human and pig pancreatic amylases in complex with carbohydrate-based inhibitors. The structural aspects of proteinaceous a-amylase inhibition have been reviewed by Payan. The sequence, architecture, and structure of a-amylases from mammals and insects are fairly homologous and mechanistic insights from mammalian enzymes can be used to elucidate inhibitor function with respect to insect enzymes. The architecture of a-amylases comprises three domains. Domain A contains the residues responsible for catalytic activity. It complexes a calcium ion, which is essential to maintain the active structure of the enzyme and the presence of a chloride ion close to the active site is required for activation. 

Contacts with the catalytic residues, in combination with hydrophobic interactions, are also observed in the complex of an insect a-amylase with the Ragi bifunctional a-amylase/trypsin inhibitor (RBI) [174]. Conversely, the mechanism of inhibition of barley a-amylase by the barley a-amylase/subtilisin inhibitor (BASI) did not involve direct contact between inhibitor residues and the catalytic site [175]. The inhibitor sterically blocks the catalytic site, but does not extend into it. A cavity is created, which is occupied by a calcium ion coordinated by water-mediated interactions with the catalytic residues. 

Structural analyses from X-ray models and predicted super-secondary models imply that CGTase structure is primarily a super-set of a-amylase structure. The active sites and calcium binding sites of a-amylase are believed to reside in the (p a)s barrel and P-strand loops of domains A and B. The various P-strand loops of the (p a)s barrel are also purported to be involved in starch binding. The antiparallel P-sheet (domain C) is hypothesized to possess starch binding capability. 

Liquefaction - Lab-Scale. 35% DS com starch slurries were liquefied with the CGTase at a dose of 4.46 Phadebas units/gram DS starch at pHs 4.5-5.5 for 14 minutes at 105 C (primary liquefaction) and for 4 hours at 90 (secondary liquefaction) +/- 40 ppm calcium. Final volumes were 5-10 ml. Termamyl and Bacillus stearothermophilus alpha-amylase were run as controls at pHs 6.2 and 5.8, respectively in the presence of 40 ppm calcium. 

The results demonstrated that the CGTase is able to liquefy com starch at any pH in the range 4.5-5.5 (Table I). Liquefaaion was considered positive if the starch syrup was pourable. The starch was liquefied to a negligible dextrose equivalent (DE) i.e., without the formation of reducing sugars as expected with a CGTase. The presence of calcium was not required. The B, stearothermophilus amylase, on the other hand, provided suitable liquefaction only at pH 5.5 and calcium was required, but still not optimal as evidenced by the results obtained at pH 5.8. 

Glucose isomerase has a higher pH optimum than is required in the preceding starch liquification and saccharification steps so that pH adjustment is necessary. Also the -amylase used to cany out saccharification requires calcium ions for full activity, but calcium inhibits glucose isomerisation, necessitating its removal by ion-exchange treatment prior to isomerisation. 

Acetylcholine is involved in many aspects of the regulation of the cardiovascular system. Thus, it may also play a role in the control of intercellular communication. Very early in gap junction research the effect of acetylcholine as an important transmitter on gap junction conductance has been investigated. First, Petersen and Ueda [1976] demonstrated an increase in junctional resistance in pancreatic acinar cells following the application of acetylcholine. Concomitantly, the release of amylase was stimulated. A minimum concentration of 1 pmol/l acetycholine was required to evoke uncoupling. The next question was, how is the acetylcholine effect mediated Calcium has been considered to contribute to the mechanism of action [Iwatsuki and Pertersen,... 

Figure 12-6 Drawing showing the overall polypeptide chain fold and relative positioning of the three structural domains of human pancreatic a-amylase. Also drawn are the locations of the calcium and chloride binding sites. Overlaid is the placement of a modified form of the inhibitor acarbose (p. 607) that binds in the active site cleft. MolScript drawing courtesy of G. Sidhu and G. Brayer.

Optional Resuspend the pellet in 50 ml of 20 mM HEPES buffer, pH 6.9/2 mM calcium chloride. Incubate with 200 U porcine pancreatic a-amylase at 40°C for 1 hr with stirring. Filter on 1 l- im mesh in a Buchner funnel. Wash twice with 50 ml HEPES/calcium chloride buffer and combine the fdtrates. Dialyze against distilled water as above (step 3) and freeze dry and weigh as described in Basic Protocol 2, steps 14 to 16. 

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